Having an obnoxious cameraman on found footage is the equivalent of seated next to a loud texting person in cinema. Extinction has a couple good moments and the setting is presentable, but almost half of the movie is spent on bickering. If it's for realism of human drama, it's doubtful that actual documentary people would argue as much and the banter is not exactly appealing. For the encounter with alleged monster, it has so little impact since the effect is far from compelling, so barely anything works in Extinction.
The film follows the journey of scientists and filmmakers to the depth of Amazon. They soon find out that the forest hides a very insidious secret. The use of found footage is mainly to create a sense of involvement for audience, yet the movie has a very confrontational cast. Nearly everyone would mumble in antagonizing manner almost in every scene, especially the cameraman James who is utterly annoying.
He would instigate people and react poorly when interacting with others. It's probably for humor purpose, but it gets tiring very fast. There are the rudimentary comments on the existence of creature which are plodding the already uninteresting endeavor. Some scenes involving actual fauna is a bit better to establish the authenticity, though these are few between all the squabbles.
As expected there would be unclear shots as the monster eventually reveals itself. It's not half bad since a couple of these instances are engaging. However, the effect for said monster is not convincing. The movie doesn't have the luxury of smooth mix of usual camcorder view and CG like Troll Hunter or Cloverfield. Not to mention the cast is unfriendly, it won't garner much sympathy.
In the end, Extinction doesn't offer an amusing journey, let alone the grandeur encounter the poster falsely advertises.